The present invention relates, in general, to remotely-operated, manipulative devices and relates, more particularly, to underwater or sub-sea, remotely-controlled, powered manipulator arms.
In recent years the use of manned and unmanned underwater apparatus to explore and develop natural resources has increased dramatically. In the petroleum industry, for example, off-shore drilling has required both manned apparatus (submersibles) and unmanned underwater apparatus (robotic devices) which are capable of performing a wide variety of manipulative tasks. Typically such apparatus includes one or more remotely operated, powered arms which have a terminal device, such as claws, pincers or jaws, which are analogous to a human hand. The manipulator arms are usually jointed or have several axes of movement and may be controlled in a preprogrammed manner or by a remotely-operated input device. Such manipulator assemblies are exposed to very adverse environmental conditions, particularly when operated in bodies of salt water at substantial depths, which is the normal operating environment for most off-shore oil exploration and recovery equipment.
Prior underwater, electromechanical manipulator apparatus have typically employed a D.C. motor coupled to a hydraulic pump as the primary power for actuation or moving of the arm assemblies. The hydraulic pumps are coupled to a hydraulic circuit employing solenoid valves to control displacement of the manipulator arms and operation of the claws or jaws on the end of the arms.
If these prior art solenoid based manipulator systems are relatively simple, the operating characteristics have been found to be poor. The smoothness and dexterity of movement with which the arm and claws can be manipulated are not satisfactory for many applications. In order to attempt to have a smoothly operating solenoid valve- based system, the valving and pump controls can be made very complex, but the resulting complexity substantially increases cost and the incidence of breakdown.
Another prior art approach to underwater manipulative assemblies is to employ a D.C. motor-feedback servo amplifier system in which the motor directly drives the mechanical elements in the arm. Such a direct coupling of the D.C. motor to the mechanical manipulator elements has been found to require extremely close tolerances with attendant undesirable cost. Moreover, there are substantial shock-loading problems in the gearboxes of such systems.
A remotely operated, underwater manipulator assembly should be capable of smooth motion over a wide speed range. Thus it should be able to move uniformly and smoothly at low speeds for precise work and smoothly at high speeds for rapid arm positioning. Underwater manipulator assemblies also should be able to exert a variable force at any of the speeds in its range of operating speeds. Moreover, a remotely operated underwater manipulator arm or assembly should have the capability of simultaneous and cooperative motion in two or more directions to give full freedom of movement of the terminal device or gripping jaws. The combination of smooth functioning over a wide speed range, variable force throughout the range, and multidirectional movement provides an underwater manipulator arm assembly which begins to closely approximate the motion and dexterity of a human arm and hand.